The present application relates to a method and process for the production of electrically superconducting films, and more particularly to the production of thin films of superconducting oxides, for example, Perovskite type oxides commonly referred to in the art as 1-2-3 compounds.
Recently it has been found that a remarkable improvement of the critical current densities of Perovskites is obtained if epitaxial cuprate Perovskites, such as the YBa.sub.2 Cu.sub.3 O.sub.7, are utilized in the form of thin, oriented films.
Typically thin films, or layers of such Perovskite-type oxide materials are produced by depositing a precursor of the superconducting material on heated substrates, usually at temperatures in the range of 400.degree. to 800.degree. C. The deposition process is carried out under vacuum and an initial thin amorphous film, desirably comprised of oxides containing the metallic elements present in a weight ratio of 1:2:3 based on the atomic mass of Y, Ba and Cu, is deposited on the substrate. Suitably the film may be deposited on the substrate by sputtering using a magnetron, or by evaporation using an excimer laser. The Perovskite starting materials may be supplied as separate sources, or as a single composite source. Unfortunately, precise resulting Perovskite compositions were difficult to obtain and control. In addition, the ratios within the compositions being deposited could not easily and rapidly be cultured. The structure of the precursor initially formed film, is subsequently converted into a superconducting Perovskite-like material having an orthorhombic structure, by subsequent treatment steps. For example, the film may be first heat treated, or annealed, over a period of time at temperatures ranging between about 700.degree. and about 900.degree. C. and subsequently the oxygen content and the desired structure the heat treated film are adjusted to the desired levels by an additional heat treatment step, usually carried out at temperatures in the range of between about 500.degree. and to about 600.degree. C., in an oxygen atmosphere.
Examples of the prior art relating to the use of pulsed laser beams to produce thin films of Perovskite-type superconducting oxides may be found in Materials Research Society Proceedings, Volume 99, 1988, pages 303-306; 327-331; 343-346; 700-702; 707-710, and 735-738; Solid State Technology, December, 1987, pages 39-41, and; Applied Physics Letters, Volume 51, No. 22, November, 1987, pages 619-621 and 1845-1847.